Various medical procedures require the precise localization of a three-dimensional position of a surgical instrument within the body in order to effect optimized treatment. For example, some surgical procedures to fuse vertebrae require that a surgeon drill multiple holes into the bone structure at precise locations. To achieve high levels of mechanical integrity in the fusing system and to balance the forces created in the bone structure it is necessary that the holes are drilled at the correct precise location. Vertebrae, like most bone structures, have complex shapes made up of non-planar curved surfaces making precise and perpendicular drilling difficult. Conventionally, a surgeon manually holds and positions a drill guide tube by using a guidance system to overlay the drill tube's position onto a three dimensional image of the bone structure. This manual process is both tedious and time consuming. The success of the surgery is largely dependent upon the dexterity of the surgeon who performs it.
Limited robotic assistance for surgical procedures is currently available. For example, the da Vinci medical robot system (Intuitive Surgical Inc., Sunnyvale, Calif.) is a robot used in certain surgical applications. In the da Vinci system, the user controls manipulators that control a robotic actuator. The system converts the surgeon's gross movements into micro-movements of the robotic actuator. Although the da Vinci system eliminates hand tremor and provides the user with the ability to work through a small opening, like many of the robots commercially available today, it is expensive, obtrusive, and the setup is cumbersome. Further, for procedures such as thoracolumbar pedicle screw insertion, these conventional methods are known to be error-prone and tedious.
One of the characteristics of the da Vinci system that makes it error prone is that, like many of the current robots used in surgical applications, it uses an articular arm based on a series of rotational joints. The use of an articular system creates difficulties in arriving at a precisely targeted location because the level of any error is increased over each joint in the articular system.